How Do Different Blood Types Affect Pregnancy?

Before planning pregnancy, a women should find out about their blood type. There are four different types, A, B, AB and O. Additionally, women can also have a Rh factor, (specifically Rhesus D antigen), which appears when protein appears on the surface of the blood. Women who do have a Rh factor, they are deemed positive, like A+, B+, AB+ and O+. Others who do not, are Rh negative, mainly, A-, B-, AB- and O-.


Medical science has proof that blood type and Rh factor of a pregnant woman and the father of her baby can affect what blood type the baby has. It can influence the antibodies in the mother’s body as an auto-immune response to foreign matter such as bacteria, sperm and even embryo. This article by Brooke Tasovac talks about how pregnancy is affected if the blood type of the mother and the fetus are different.

To cite an instance, when a Rh negative women have a baby with Rh positive blood, it can trigger off the auto-immune system which would treat the Rh proteins in the baby’s blood as foreign bodies. This Rh incompatibility can lead the anti-bodies in the mother to attack, giving birth to a condition called Rhesus disease.

The problem is not limited to difference of Rh proteins, there can also be a problem if the mother’s blood type is O and her baby is A or B. The mother’s body would produce anti-bodies against the baby’s red blood cells when the blood mixes. This is called ABO incompatibility. 1

Risk Factors In Blood Type Incompatibility

When a woman is pregnant for the first time, the baby is generally protected from the blood of the mother until birth. This is because the mother’s blood cannot cross the placenta, but the baby’s blood can get into the mother’s blood circulation. However, sometimes, there are instances wherein the baby’s blood and mother’s have mixed and have caused the following complications:

  1. Miscarriage
  2. An injury leading to bleeding
  3. After amniocentesis (blood is taken from the umbilical cord for testing)
  4. After CVS (a sample of the placenta is taken for testing)
  5. Ectopic pregnancy

In these cases, the antibodies have developed an immune response leading the baby to have anaemia and severe jaundice.

In Rh incompatibility, whenever a woman is pregnant with Rh positive baby in the future, antibodies would be produced in higher amounts.

However, in the case of ABO incompatibility, the situation does not become serious with subsequent pregnancies. ABO incompatibility still can affect a baby until all the antibodies passes out of the baby’s system after they are born.

Treatment Options Available

Because the baby’s blood group cannot be determined inside the womb, all Rh negative women receives anti-D injections during her pregnancy term to prevent onset of Rhesus disease at 28 and 34 weeks. Once the baby is born, the cord blood is collected to check the blood group of the baby, and if found to be Rh positive, another injection is given.

These injections are found to be effective in stopping the Rh antibodies developing and makes it possible for pregnant women to be pregnant again without Rh incompatibility. If the baby is born and found to be Rh negative, no injections are needed.

If the mother has been diagnosed with Rhesus disease, the doctor maintains regular check-ups of the fetus to ensure its health. This is done through ultrasound. However, if at any time, the baby’s blood count is found to be too low, special blood transfusion (either before or after birth) can be given to the baby through the umbilical cord to stop the depletion of RBCs. Brace yourself, as sometimes, the doctors might decide to induce pre-term labor. However, this is only for extreme situations and the anti-D injections are quite effective.

In ABO incompatibility, there are precautions that would protect the baby, however, if the baby shows any sign of anaemia in-utero, or is extremely jaundiced, they are given phototherapy to help break down the chemicals in the blood. Blood transfusions might also be required if they are too anaemic. These are done only after the baby is born.

How does it affect the health of the mother?

The mother’s health is not affected by blood type incompatibility, however, if pregnant women have bleeding of any kind that should be immediately brought to notice of their doctors.